Activation of compressed wood



Patented June 13, 1939 PATENT OFFICE 2,162,366 ACTIVATION OF COMPRESSEDWOOD Maurice E. Barker and Robert S. Brown, Edgewood, Md.

no Drawing. Application April 21, 1932, Serial No. 607,901

15 Claims.

(Granted under the act of March 3, 1883, as amended Apr--30, 1928: 3'100. G. 757) This invention described herein may be manuiactured and usedby or for the Government for Government purposes, without the payment tous of any royalty thereon.

5 Our invention relates to a processfor making charcoal, and moreparticularly has reference to a method of producing adense, active andhighly retentive gas adsorbent charcoal from wood of any kind, whichheretofore has been possible only by the use of very dense tropicalwoods.

We are well aware that there are many processes for producing activecharcoal from wood, including among them impregnating the wood with anacid prior to carbonization, the practice of selectively oxidizing woodto increase the adsorption power of wood charcoal, and various methodswhich treat wood charcoal with steam or air at elevated temperatures.However, all of these processes produce a charcoal from ordinary woodcontaining many large pores, with a resulting low gas retentive value ofthe charcoal, although large amounts of gas may be adsorbed at highconcentrations.

To overcome this difficulty, the art made use of Q5 the expedient ofcompressing the carbonaceous material employed into blocks or briquettesto increase its density. Such processes have been limited chiefly to theuse of a raw material such as coal or charcoal fines, and have employeda binder for holding together the particles of the material treated. Inaddition, however, attempts have been made to compress wood fibers orother disintegrated wood products into blocks which have beensubsequently carbonized, it being necessary to keep the wood as used inthis form under pressure during carbonization.

It will hence be apparent that the major, object of our invention is theprovision of a process for the production of a dense, active, and highlyre im tentive gas adsorbent charcoal from ordinary Wood.

An equally important object of our invention is to provide a process forthe formation of charcoal from wood blocks.

Another object of the invention is the provision of a method for formingcharcoal from wood blocks, these being first thoroughly dried and thencompressed so as to increase their density prior to their carbonization.

Still another object of our invention is to devise a method of forming ahighly active gas adsorbent charcoal from solid wood blocks which havebeen impregnated with a dehydrating agent, then dried and compressedprior to' carbonization.

55 Yet another object of our invention is the provision of a process forproducing an activated charcoal from compressed wood blocks impregnatedwith a dehydrating agent which includes carbonizing the blocks byheating them in the presence of air and then heating them at higher 5temperatures in carbondioxide gas containing a little water vapor.

A further object of our invention is the provision of a process forforming activated charcoal from compressed wood blocks impregnated witha. 10 dehydrating agent which includes carbonizing the blocks by heatingin the presence of air, then increasing the temperature of the heattreatment while heating in the presence of carbon dioxide with a littlewater vapor, crushing the blocks so 1 treated and activating the blocksin a stream of preheated carbon dioxide at activation temperatures.

A still further object of our invention is the provision of a processfor the formation of dense, 20 active charcoal from compressed woodblocks which have been impregnated with a dehydrating agent and whichafter carbonization and after activation in a stream of preheated carbondioxide gas are cooled in a stream of carbon 25 dioxide.

With these and other objects in view, the invention consists in themethod to be hereinafter set forth and claimed, with the understandingthat the steps. thereof and the treatment of the 80 raw materialsemployed may be varied, for it is apparent that many changes may be madetherein, by those skilled in the art, without departing from the spiritof the invention or exceeding the scope of the appended claims.

Broadly, the invention contemplates the provision of a process for theproduction of a dense, active, and highly retentive gas adsorbent woodcharcoal. One manner of practically effecting the concept of theinvention is to impregnate 40 dried wood blocks with a dehydratingagent, then again drying these blocks and finally compressing them so asto increase their density.

' The compressed impregnated blocks are next carbonized by heating in afurnace in the presence of air for a suitable time period, after whichthey are further heated at temperatures elevated above those employed inthe first heat treatment,

6 in an atmosphere of carbon dioxide gas containing a small amount ofwater vapor.

Our invention also comprehends the crushing of the blocks treated in themanner just noted and the subjecting of he fines so obtained toactivation in a stream of preheated carbon dioxide held at activationtemperatures. After the acti- 65 vation step, the charcoal particles arecooled in -a stream of carbon dioxide and are then ready for use asadsorbent charcoal.

Before giving a complete description of our invention, it should benoted that in the activation of charcoal a primary charcoal is firstformed in which the charcoal substance has a true density of about 1.46and is without a definite X-ray diffraction pattern. After activation, agood chargas retained at zero partial pressure. Furthermore, the amountof gas retained per unit volume of the charcoal is the ultimatecriterionfor a gas I mask charcoal. This use demands a charcoal of high apparentdensity as well as possessing the desired retentive properties. Ourinvention makes possible the production of such a charcoal from ordinarywood.

We have found that useful results may be attained by cutting wood intoapproximately two inch cubes, thoroughly kiln drying, compressing thewood to from ten to twenty thousand pounds per square inch, carbonizingthe wood and finally activating by any of the known means. By such aprocess a dense active charcoal having a high retentive value can beformed.

An even better charcoal may be formed by first drying the two inch cubesof wood, impregnating these wood blocks with zinc chloride or othermetallic chlorides, drying at a temperature below 100.C., compressingthe blocks to approximately twenty thousand pounds per square inch,carbonizing and activating.

vIn following our preferred process, wood blocks which are approximatelytwo inch cubes, are first kiln dried, after which they are impregnatedwith a good grade of zinc chloride from a 25% water solution by the fullcell process.- The zinc chloride, as will hereinafter appear, acts as adehydrating agent, and while this compound has been disclosedspecifically, it is to be noted that in general any dehydrating agentmay be employed. Included among such agents are the metallic salts ofstrong acids or metallic chlorides. Similarly in some instances, it maybe found desirable to use more than one dehydrating agent as well as tovary the concentration of the dehydrating solution. The use of adehydrating agent to increase the yield of charcoal from wood is old inthe industry. Obviously, any change in the dehydrating agent employed.or its concentration, is well within the spirit of the invention and thescope of the appended claims.

Impregnation of the thoroughly dried block having been completed, theimpregnated blocks are then kiln dried, for approximately two days,being treated at temperatures Just below 100 C. From the second dryingstep. just disclosed, the blocks are then compressed for the purpose ofincreasing the density of the wood. To this end, each block is held in adie, and subjected to a pressure of approximately twenty thousand poundsper square inch.

Other pressures may be employed, for it will be obvious to those skilledin the art that a variation in the pressure employed, while compressingthe blocks, will only efl'ect their density. However, we have found thata pressure of approximately twenty thousand pounds per square inchproduces satisfactory'results with the size of blocks employed.

The compressed impregnated blocks are now ready for carbonization so asto convert them into primary charcoal, which is subsequently activated.These blocks are first heated in a muiile furnace or other standardfurnace in the presence of air at a temperature of 100 C., increasing to200 C. for twenty-four hours. After this initial heating 'step, theblocks are again heated for about twentyfour hours in carbon dioxide gascontaining a little water vapor at a temperature of about 200 C., slowlyincreasing to 800 C. The blocks are, after the second heating step,cooled out of contact with the air.

Prior to activation, and after the cooling of the compressed blocks,they are crushed so as to pass a six mesh screen and be held on a twelvemesh screen. The granules so obtained are then ready for activation, andto this end are loaded into trays, each tray containing granules to adepth of approximately one inch and are activated for about two hours ina stream of. preheated carbon dioxide at 800 C. to 850 C. Following thisprocess the charcoal does not require washing since the metallicelements which remain are desirable in the final product thus obtained.

It should be observed that in carrying out the process, the raw materialemployed is in the form of solid wood blocks, which blocks are notdisintegrated wood products or wood fibers. While we have hadconsiderable success with wood blocks in the form of two inch cubeswhich have been compressed under a pressure of from ten to twentythousand pounds per square inch, it is to be understood that theinvention is not limited to this size of block or, as already pointedout, to any particular pressure.

In our process; it may be observed that the zinc chloride acts as adehydrating agent and changes the wood to charcoal and water in thefirst part of the carbonization, thereby increasing the weight yield ofcharcoal. The zinc chloride, during the heating at 700 C. to 750 C. inthe presence of carbon dioxide, is broken down to zinc oxide, and thechlorine thereof combines with the hydrocarbons present in the charcoalbeing treated. At the higher temperatures of 800 C. to 850 0. used, thechlorinated hydrocarbons which have been formed are broken down andgiven oil, additional hydrocarbons'reduce the zinc oxide, some of thezinc is vaporized, and graphite is formed in exceedingly small particlesizes.

Active charcoal produced by our process using any wood as a raw materialhas an apparent density of from 0.40 to 0.55. Compared to this should benoted the density of 0.25 to 0.30 for the product obtained by practicingthe methods heretofore outlined as used by the prior art.

At the same'time, the gas retentivity of charcoal, prepared inaccordance with our invention, is about double that of any charcoalproduced from wood by following the teachings of the prior artpreviously noted.

It will hence be appreciated that by following our process a dense,active and highly retentive gas adsorbent charcoal may be produced froma relatively inexpensive and an abundant raw material, namely, wood.Moreover, in carrying out the process, the substances used in treatingthe raw material employed are also of an inexpensive nature while theprocess steps carried out are 01 such simple character that they may beperformed with standard apparatus.

While we have'shownand described'the preferred manner of carrying outour invention, we wish it to be understood that we do not confineourselves to the precise method set forth, byway of illustration, as itis apparent that many changes and variations may be made therein,without departing from the spirit of the invention, or exceeding thescope of the appended claims.

We claim:

1. A process of producing charcoal, includin the steps of impregnatingwood blocks in their natural state with a dehydrating agent,.compressingthe impregnated blocks under a pressure of 10,000 pounds per square inchor upward, and carbonizing the blocks by heat treatment.

2. A process of producing activated charcoal, including the steps ofimpregnating wood blocks with a dehydrating agent, compressing theimpregnated blocks under a pressure of 10,000

7 pounds per square inch or upward, and carbonizing the blocks by firstheating them in air and then heating them in carbon dioxide attemperatures elevated above those first employed.

3. A process of producing activated charcoal including the steps orimpregnating wood blocks with a dehydrating agent, compressing theimpregnated blocks under a pressure 01' 10,000 pounds per square inch orupward, and carbonizing the blocks by first heating themv in air andthen heatingthem in carbon dioxide at temperatures elevated above thosefirst employed, and cooling the blocks out of contact with the air.

4. In a process for forming wood charcoal, the steps of impregnatingwood blocks with zinc chloride and then compressing the blocks under apressure of 20,000 pounds per square inch, prior to oarbonization. l

5. A process for producing a dense primary charcoal suitable foractivation to a gas adsorbent material, including the steps ofimpregnating non-comminuted wood blocks with a dehydrating agent, highlycompressing the impregnated blocksto a density 01 1.0 or more, andcarbonizing the blocks by heat treatinent.

6. In a process for forming primary wood char-' coal, the steps ofimpregnating wood blocks with a metallic chloride, and then highlycompressing" the blocks to a density of 1.0 or more prior tocarbonization.

7. In a process for forming wood charcoal, the steps of impregnating thewood blocks with zinc chloride, and then compressing the blocks under apressure of approximately 20,000 pounds per square inch and thencarbonizing the blocks in two stages, the second stage thereof being ata higher temperature than the first stage.

8. A process for forming dense primary charcoal from wood blockscomprising the steps of kiln-drying the blocks, impregnating the blockswith a dehydrating'agent, redrying the blocks, compressing theimpregnated blocks to a density of 1.0 or more, and carbonizing thecompressed blocks by heat treatment.

9. The method of forming a primary charcoal 1 from non-comminuted woodblocks comprising the steps of kiln-drying the blocks, impregnating theblocks with a dehydrating agent, redrying the blocks in air atapproximately 100 (3., highly compressing the impregnated blocks to adensity of 1.0 or more, and carbonizing the compressed blocks by heattreatment.

10. The method of forming activated charcoal from wood blocks comprisingthe steps of kilndrying the blocks, impregnating the non-comminuatedblocks with a dehydrating agent, redrying the blocks in air, compressingthe impregnated blocks to a density of 1.0 or more, and carbonizing thecompressed blocks by first heating them in air and then heating them incarbon dioxide at temperatures elevated above those first employed.

11. A process of producing activated charcoal, including the steps ofimpregnating non-comminuted wood blocks with zinc chloride, highlycompressing the impregnated blocks to a density of 1.0 or more,carbonizing the blocks by first heating them in air at approximately 100C., and

then heating them in carbon dloxide at temperatures elevated above thosefirst employed.

12. A process otproducing activated charcoal,

including the steps of impregnating non-comminuted wood blocks with adehydrating agent,

highly compressing the impregnated blocks to a density of 1.0 or more,and carbonizing the blocks by first heating them in air, then heatingthem in carbon, dioxide at temperatures elevated above those firstemployed, and cooling the blocks out of contact with air.

13. A method of forming activated charcoal, comprising the steps ofkiln-drying non-comminuted woodblocks, impregnating the blocks with adehydrating'agent, redrying the blocks in air, highly compressing theimpregnated blocks to a density of 1.0 or more, carbonizing the blocksby heating to approximately 200 C. in air, fol--v lowed by{ heating atgradually increasing higher temperatures in carbon dioxide gas, coolingthe carbonized material out of contact with air, crushing the carbonizedmaterial, activating the crushed particles in a stream 0! preheatedcarbon dioxide at 800-900 C. for two hours, and cooling the particlesout of contact with air. I

14. A process of producing dense primary charcoal which comprisescutting blocks 0! wood, compressing the blocks under a pressure or10,000

pounds per square inch or upward, and carbonizing the compressed blocksby heat treatment.

15. In a process for forming wood charcoal, the steps or impregnatingwood blocks with a metallic chloride, and then compressing the blocksunder a pressure of 10,000 to 20,000 pounds per square inch prior tocarbonization.

MAURICE E. BARKER. ROBERT 5. BROWN.

